Turning switch is a common switch configuration. The ratchet wheel positioning mechanism will help turning switch to effect the mechanical configuration of turning switch implementing switchover from one control-position to next control-position and then instantly to lock the mechanical configuration at the next control-position, when there are several control positions needed to be controlled by a turning switch.
Generally, the ratchet wheel mechanism of turning switch has two main functions: Non-returning and positioning function, i.e. to prevent turning switch from coming back to its previous control-position and to lock turning switch at a certain control-position in turning operation; Snap-jumpiness function to indicate the turning switch already being turned to position, i.e. when the turning switch is turned to a certain control-position, the switch configuration may send out a snap or a jumpiness to cause operator be able to distinctly perceive the turning switch already being turned to an expected position in order to prevent the operator from stopping the turning operation before achieving next switch control-position or from continuing the turning operation after already achieving an expected switch control-position.
Now, a description about the functions of a ratchet wheel mechanism of the prior art in turning switch is made through FIGS. 1A to 1E.
FIG. 1A is a schematic diagram to show said ratchet wheel mechanism 100 at still (initial) position, wherein comprising: ratchet wheel 110 co-axial with camshaft and pawl device 120. Ratchet wheel 110 has 6 ratchet teeth 111 (111.A, 111.B, 111.C, 111.D, 111.E, 111.F) to divide the circular rim into six equal segments. Pawl device 120 has two transversal pawl arms 121 (121.A, 121.B) symmetrically disposed along height direction (relative to the axis of camshaft), on two transversal pawl arms 121 (121.A and 121.B) respectively exists a pawl 122 (122.A, 122.B), they are symmetrically disposed along height direction, transversal pawl arms 121 and pawls 122 are made from resilient material, such as plastic, etc. Ratchet wheel 110 and pawl device 120 may be made from Nylon. As shown in FIG. 1A, ratchet wheel 110 and pawl device 120 are matched each other at a certain control-position. Saying concretely, at this control-position, upper ratchet pawl 122.A is between two adjacent ratchet teeth 111.A and 111.B, lower ratchet pawl 122.B is between two adjacent ratchet teeth 111.D and 111.E. So that ratchet wheel 110 will be locked at this control-position. As shown in FIG. 1A, ratchet teeth 111 (111.A, 111.B, 111.C, 111.D, 111.E, 111.F) and pawls 122 (122.A, 122.B) are circular-arc shape.
FIG. 1B shows said ratchet wheel 110 starting to be being turned from still (initial) position shown in FIG. 1A toward next control-position. As shown in FIG. 1B, when the operator turns the knob (not shown in the Figure) counterclockwise, which is disposed at one end of ratchet wheel 110, ratchet wheel 110 starts to turn counterclockwise resulted in ratchet tooth 111.B also being turned. In this time, the circular-arc shape surface of ratchet tooth 111.B will act an outward thrust on the circular-arc shape surface of pawl 122.A at their contact place, then due to the elasticity of transversal pawl arm 121.A, upper pawl 122.A moves outward and resulted in that an outward elastic bending deformation of transversal pawl arm 121.A will occur along with the outward movement of upper pawl 122.A. Similarly, when the counterclockwise turning of ratchet wheel 110 causes ratchet tooth 111.E to turn, the circular-arc shape surface of ratchet tooth 111.E will act an outward thrust on the circular-arc shape surface of lower pawl 122.B at their contact place, then due to the elasticity of transversal pawl arm 121.B, lower pawl 122.B moves outward resulted in that an outward elastic bending deformation of transversal pawl arm 121.B will occur along with the outward movement of lower pawl 122.B. As shown in FIG. 1B, for the interactions between both the circular-arc shape surfaces of upper pawl 122.A and ratchet tooth 111.B and between both the circular-arc shape surfaces of lower pawl 122.B and ratchet tooth 111.E, so that when the top points of the circular-arc shape surfaces of upper pawl 122.A and lower pawl 122.B respectively approach to the top points of the circular-arc shape surfaces of ratchet tooth 111.B and ratchet tooth 111.E, if knob is loosen by the operator (or the operator does not apply any force to knob), the resilient forces respectively produced by the elastic bending deformation of transversal pawl arm 121.A and by that of arm 121.B will compel ratchet tooth 111.B and ratchet tooth 111.E still to comeback to their respective original control-position. Namely, in this time the operator has to act force continuously to turn ratchet wheel 110 and cannot stop.
FIG. 1C is a schematic diagram of a typical ratchet wheel mechanism when a cam is turned just to hung-up point to show said ratchet wheel 110 at the position shown in FIG. 1D being turned continuously toward next control-position. At the position shown in FIG. 1B, the operator continuously turns ratchet wheel 110 counterclockwise, upper pawl 122.A continuously moves outward to cause the elastic bending deformation of transversal pawl arm 121.A continuously increasing, then the top point of circular-arc shape surface of upper pawl 122.A coincides with the top point of circular-arc shape surface of ratchet tooth 111.B. Similarly, lower pawl 122.B continuously moves outward to cause the elastic bending deformation of transversal pawl arm 121.B continuously increasing along with the counterclockwise turning of ratchet wheel 110, then the top point of circular-arc shape surface of lower pawl 122.B coincides with the top point of circular-arc shape surface of ratchet tooth 111.E. At this time, the outward elastic bending deformation of two transversal pawl arms 121 (121.A and 121.B) increases to maximum. For the resilient forces respectively acted on the top point of the circular-arc shape surfaces of ratchet teeth 111.B and 111.E by the top point of the circular-arc shape surface of upper pawl 122.A and by the top point of the circular-arc shape surface of lower pawl 122.B just pass through the center of ratchet wheel 110, so they cannot yield turning moment for ratchet wheel 110. When the top points of the circular-arc shape surfaces of upper pawl 122.A and lower pawl 122.B respectively coincide with the top point of the circular-arc shape surface of ratchet tooth 111.B and with that of ratchet tooth 111.E, if knob is loosen by the operator (or the operator does not apply any force to knob), ratchet wheel 110 will stop at this position and keep in equilibrium, notwithstanding this position is not the expected next control-position, i.e. ratchet wheel 110 keeps in equilibrium and stop at a wrong position. Such phenomenon means there exists a hung-up point between two adjacent switch control-positions, and then to cause the turning switch bringing control failure.
FIG. 1D is a schematic diagram of a typical ratchet wheel mechanism after a cam going over hung-up point to show said ratchet wheel 110 at the position shown in FIG. 1C continuously being turned toward next control-position. At the position shown in FIG. 1B, the operator continuously turns ratchet wheel 110 counterclockwise, transversal pawl arm 121.A starts to move inward, then to cause upper pawl 122.A moving toward next control-position. Similarly, transversal pawl arm 121.B also moves inward along with the counterclockwise turning of ratchet wheel 110, then to cause lower pawl 122.B moving toward next control-position. For the interactions between both the circular-arc shape surfaces of upper pawl 122.A and ratchet tooth 111.B and between both the circular-arc shape surfaces of lower pawl 122.B and ratchet tooth 111.E, so that when the top points of the circular-arc shape surfaces of upper pawl 122.A and lower pawl 122.B respectively somewhat depart from the top points of the circular-arc shape surfaces of ratchet tooth 111.B and ratchet tooth 111.E, even though in this time the force acted on the knob is decreased (or no force acted on the knob), the resilient force produced by the elastic deformation of transversal pawl arms 121.A and 121.B yet will help to push ratchet teeth 111.B and 111.E (or push teeth 111.B and 111.E directly by resilient force itself) to next control-position, i.e. ratchet wheel 110 may be turned through a smaller force acted by the operator (or the operator does not act any force).
FIG. 1E is a schematic diagram of a typical ratchet wheel mechanism when a cam turning 60° to show said ratchet wheel 110 at the position shown in FIG. 1E continuously being turned to achieve next control-position. As shown in FIG. 1E, ratchet wheel 110 and pawl device 120 are matched each other at the next control-position. Saying concretely, at this control-position upper pawl 122.A is between ratchet teeth 111.B and 111.C; lower pawl 122.B is between ratchet teeth 111.E and 111.F. So that ratchet wheel is locked at the next control-position.
The ratchet wheel mechanism introduced above has following shortcomings: (1) Ratchet wheel may stop at a hung-up point between two adjacent switch control-positions, then to cause control failure occurring for the turning switch, the phenomenon of hung-up point especially is able to occur, if a large angle is included between two adjacent ratchet teeth (such as not less than 60°). (2) The ratchet wheel mechanism, introduced above, has a low working efficiency, for the frictional force existing among the contact surfaces of ratchet teeth of ratchet wheel and pawls. (3) More larger turning moment is needed for the turning switch having more loops to control, hand handle in operation also is not comfortable; Furthermore, the applied force is uneven and the operation is unsteady due to the interference of interior electricity-conductive contact spring of the turning switch.